PRE-Q Chemistry Flashcards
1
Q
Describe the properties of a solid and explain the reason to these properties
A
Solids have a fixed shape and cannot flow - particles are unable to move from place to place. Solids cannot be compressed or squashed - particles are tightly packed together and have no space to move into.
2
Q
Describe the properties of a liquid and explain the reason to these properties
A
Liquids flow and take the shape of their container - the particles can move around each other. Liquids cannot be compressed or squashed - the particles are close together and have no space to move into.
3
Q
Describe the properties of a gas and explain the reason to these properties
A
Gases flow and completely fill their container - the particles can move quickly in all directions. Gases can be compressed or squashed - the particles are far apart and have space to move into.
4
Q
Name of the change of state from solid to liquid
A
Melting
5
Q
Name of the change of state from liquid to solid
A
Freezing
6
Q
Name of the change of state from gas to solid
A
Reverse Sublimation or Deposition
7
Q
Name of the change of state from solid to gas
A
Sublimation
8
Q
Name of the change of state from liquid to gas
A
Evaporation
9
Q
Name of the change of state from gas to liquid
A
Condensation
10
Q
What does a heating curve show? Name the 5 stages.
A
The change of states as substance is heated over time. Solid heating, solid melting, liquid heating, liquid boiling, gas heating.
11
Q
What does a cooling curve show? Name the 5 stages.
A
The changes of states as substance is cooled over time. Gas cooling, gas condensing, liquid cooling, liquid freezing, solid cooling.
12
Q
What is the Kinetic Theory of an Ideal Gas?
A
An attempt to explain the observable properties of gases. No real gas meets all of the properties of an ideal gas.
13
Q
Name the 5 properties of an Ideal Gas
A
- Gases are made of particles in constant random motion
- The particles move very fast and collide with each other and the walls of their container with perfectly elastic collisions. (They bounce but lose no energy)
- The particles are negligible in size when compared with the space between them
- There are no attractive or repulsive forces between the particles
- The average kinetic energy of the molecules is proportional to the temperature of the gas
14
Q
What is absolute zero?
A
The theoretical temperature (which can never be reached) at which all particle motion stops. (-273 degrees celcius or 0 Kelvin)
15
Q
What is gas pressure and how is it measured?
A
The result of collisions of gas particles with the walls of their container. A pressure gauge measures pressure by quantifying these collisions. Measured in atmospheres (atm) or Pascals (1.0 Pa = 1.0 N/m^2)
16
Q
What is Brownian Motion?
A
The random movement of particles in both liquids and gases (fluids). They do this because they are bombarded by the other moving particles in the fluid. Larger particles can be moved by light, fast-moving molecules.
17
Q
What is an element?
A
A pure substance consisting of only one type of atom
18
Q
What is a compound?
A
Pure substances containing two or more elements chemically bonded together
19
Q
Name the 3 sub-atomic particles and their properties
A
Protons - found in nucleus, have a positive charge and a relative mass of 1
Neutrons - found in most nuclei, have no charge and a relative mass of 1
Electrons - found surrounding the nucleus, have a negative charge and negligible mass
20
Q
What does the Proton (Atomic) number show?
A
The number of protons in the nucleus.
21
Q
What does the Nucleon (Mass) number show?
A
Sum of the number of protons and the number of neutrons in the nucleus
22
Q
What are isotopes?
A
Atoms of the same element with different numbers of neutrons.
23
Q
How do isotopes differ from their normal elements?
A
They have identical chemical behaviour and thus react in the same way however, they can have slightly different physical properties due to the number of neutrons being different - this can include a slight difference in melting point or boiling point, or even radioactive ability
24
Q
Name two types of isotopes
A
Radioactive and Non-radioactive
25
What are radioisotopes?
Isotopes that are said to be radioactive. They are said to decay or disintegrate.
26
Name and identify the properties of 3 different radiation
alpha - cannot pass through skin. but are extremely dangerous when taken into body
beta, gamma - can pass through skin quite easily and may damage or kill cells, causing illness, or cause changes in the cell DNA which may cause cancer
27
What is the mass of 1 hydrogen atom?
1.67 x 10^-24 grams
28
What is a relative atomic mass?
The average mass of all atoms of that element relative to a standard mass (1/12 of the mass of one atom of carbon - 12). This allows for the different masses and different abundances of each type of atom of that element.
29
What is a mole?
The mole is defined as the amount of substance of a system that contains as many "elemental entities" as there are atoms in 12g of carbon-12. 6.02x10^23 = avogadro's number
30
What is an ion?
A neutrally charged atom that has lost or gained electrons - charged particles
31
How are positive ions formed?
Positive ions form when metals lose electrons. When they do they have more protons than electrons so are positively charged overall
32
How are negative ions formed?
Negative ions are formed when non-metals gain electrons. When they do they have more negative charges in terms of electrons than positive charges in terms of protons so are negatively charged overall. NOTE - the name of the non-metal now changes to represent the ion formed
33
What is an ionic bond?
An electrostatic attraction between positive and negative ions
34
What is an ionic solid made up of?
A crystalline lattice of alternating positive and negative ions held together by strong electrostatic attraction.
35
Describe properties of an ionic solid
High melting points, do not conduct electricity when solid and are brittle.
36
Can liquid ionic compounds conduct electricity?
Yes, the ions within the compounds are free to move
37
What does isoelectronic mean?
When two atoms or ions (or compounds) have the same electron structure they are considered to be isoelectronic.
38
What is a covalent bond?
A bond formed by sharing of electrons between two non-metals.
39
How are shapes of covalent molecules formed?
The shape of the molecule is determined by the repulsion between the bonding and non-bonding electron pairs around the central atom
40
Name and describe the 5 simple shapes of covalent molecules.
Linear- 2 electron pairs around the central atom (180)
Triangular Planar - 3 electron pairs around central atom (120)
Trigonal Pyramidal - 3 electron pairs and one lone pair around central atom (107)
Tetrahedral- 4 electron pairs around central atom (109.5)
Bent - 2 electron pair and 2 lone pairs around central atom (105)
41
What is a molecular solid?
These are small molecules in which there is strong covalent bonding within the molecules. Also, between the molecules there arew eak forces (Van der Waals) which attract the molecules to each other in their solid state. Such solids have low melting points, do not conduct and are usually brittle
42
What is Van der Waals forces?
Forces of attraction which exist between all atoms and molecules. These are much weaker than all other types of bonding. Only significant in atoms and molecules which have no other types of intermolecular forces of attraction. A result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.
43
Explain how Van der Waals forces occur?
Electrons are constantly moving about
Sometimes they are more concentrated in one region that the other.
The region where they are concentrated has a slight negative charge or dipole in that instance of time. The other region which is electron deficient has a slight positive charge.
These regions between neighbouring atoms or molecules will attract each other.
The bigger the atom or molecule the bigger the Van der Waals force.
44
How are polar covalent bonds formed?
Some covalent bonds involve uneven sharing of the electron pair or pairs in the covalent bond. When the shared pair of electrons is closer to the atom of a slightly stronger attraction a polar covalent bond is formed as it gives that atom a slightly negative charge.
45
What does polarity affect?
The solubility of various types of compounds.
46
What is a hydrogen bond?
Another type of polar covalent bonds. They occur when hydrogen is bonded to an atom of oxygen, fluorine or nitrogen, forming polar bonds. Hydrogen bond are electrostatic forces of attraction between molecules which contain these highly polar bonds. H-bonds are stronger than the interactions which occur between polar covalent compounds and Van der Waals forces, but weaker than covalent bonds.
47
Explain how metallic bonds are formed?
Metal atoms give up their outermost electrons to form positive ions. These electrons then surround the positive metal ions in a sea of delocalised electrons. Metals form a 3 dimensional lattice structure. The attraction between between the positive ions and the moving "sea of mobile negative electrons" is known as the metallic bond.
48
Describe the properties of metallic solids
- varying melting points
- conduct electricity (all metals conduct)
- malleable and ductile
- lustrous (shiny)
- usually grey - exceptions include copper and gold
49
What is an alloy?
A mixture of two elements, one of which is a metal. Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone. Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than pure metal.
50
What is a Network Covalent Solid (Macromolecular Solid)?
Solids made up of very large molecules in which the atoms are bonded to each other by strong covalent bonds in 2 or 3 dimensions. These have high melting point, do not conduct and are generally brittle
51
What is an allotrope? Define the 3 allotropes of carbon
An allotrope is different physical forms of the same element. The three allotropes of carbon are diamond, graphite, and C60 (fullerene)
52
Describe the structure and property of diamond
In diamond, carbon forms 4 covalent bonds. The bonds for each carbon atom are directed towards the corners of a regular tetrahedron. These bonds are very strong, and molecule has very high melting and boiling point. Diamonds are a macromolecule (3D netweork solid). Diamond does not conduct.
53
Describe the structure and property of graphite
Graphite is made up of layers of carbon atoms that are joined in hexagonal rings where each carbon is joined to three others. Since each carbon only forms three covalent bonds the 4th electron exists between layers. These electrons are delocalised allowing graphite to conduct electricity.
54
What are the two types of bonds in graphite?
Strong covalent bonds between carbon atoms in the layers. Weak forces of attraction between layers called Van der Waals forces
55
What is C60?
The fullerenes are a large class of allotropes of carbon and are made of balls of carbon atoms. Buckminister fullerene is one type of fullerene. Its molecules have 60 carbon atoms arranged in a hollow space. It sublimes between 450-500. Exists in the form of a soft powder.
56
What is diffusion?
The random movement of liquid and gas molecules form regions of high concentration to regions of low concentration
57
Name and explain the factors which affect diffusion
1. Molecular mass- Heavy particles move more slowly (Ek=1/2mv^2)
2. Temperature- The rate of diffusion increases as temperature increases due to increased kinetic energy
3. Concentration gradient- The difference in concentration between the two areas of liquid or gas molecules are diffusing down. The greater the difference, the faster the rate of diffusion
58
Name three pieces of equipment that can be used to measure volume
Measuring cylinder, pipettes, biurettes
59
Explain how filtration works
Filtration is used to separate insoluble solids from either water or aqueous solutions. The residue cannot fit through holes in the filter paper whereas the filtrate can. (e.g. Sand/Seawater)
60
Explain how decanting works
Decanting uses density difference to separate two immiscible liquids - the denser liquid can be tapped out from the bottom first, and later the pure A substance is collected (using separating funnel)
61
Explain how chromatography works
Used to separate mixtures of substances into their components. The substances or solutes are blotted onto a line drawn in pencil on a piece of chromatography paper. This is placed in a solvent, such as water or ethanol. As the solvent rises up the paper the substance separates out into individual components. Those parts that are most soluble travel along with the solvent further up the paper.
62
What is the Rf values of each components?
The final distance of the solvent is measured and is called the solvent front. This is used to work out the Rf values of each component, these can be compared to a database which contains Rf values of hundreds of substances. (Rf = length between substance and origin divided by length between solvent front and origin
63
Explain how evaporation works
Evaporation separates a liquid from a solid but does not keep the liquid
64
Explain how distillation works
Distillation is used to separate 2 liquids by making use of their different boiling points. The liquid with the lower boiling point evaporates off first, rises and travels through a condenser where it is cooled using cold water. The gas condenses back into the liquid which can then be collected
65
Explain how fractional distillation works
The separation of two or more volatile liquids based on the differences in boiling points.
66
Explain how diffusion works
Gases diffuse at different rates. The diagram shows an apparatus that could be used to separate a mixture of gases with different molecular masses. Smaller molecules diffuse faster.
67
Explain how sublimation works
This method involves heating a mixture of two solids, one of which will sublime. The vapor is condensed, usually onto something cold. (Iodine and ammonium chloride are common laboratory substances which sublime)
68
Explain how magnetism works
Magnetic separation takes out those things which are attracted to a magnet
69
How can melting point and boiling point be used to identify a substance and its purity?
When you compare the melting points and boiling points to a data book, the substance are pure or correctly identified if values agree.
70
What does an impurity do to a liquid substance?
An impurity dissolved in a liquid will lower the freezing point and increase the boiling point
71
What is a saturated solution?
a chemical solution containing the maximum concentration of a solute dissolved in the solvent. The additional solute will not dissolve in a saturated solution.
72
Explain the structure of a periodic table
Elements are arranged in order of increasing atomic number. Groups are vertical columns numbered 1 to 0 (or alternatively 1-18) and rows are called periods in the Periodic table
73
Describe the properties of a group 1 metal
The Alkali metals
All have a metallic lattice structure
They are relatively soft metals
All have one electron in the outermost energy level which can be easily lost to form a positive ion
All react with water, producing hydrogen and forming soluble alkaline hydroxide solutions
( Na(s) + 2H20(l) = Na+(aq) + 2OH-(aq) + H2(g))
The MP and BP decrease going down the group. This is because the attractive force of the nucleus which holds the outer electron decreases as the size increases
Density increases down the group
74
Describe the properties of a group 2 metal
The Alkaline Earth Metals
All have a metallic lattice structure
They are less reactive than the preceding Group 1 elements, because two electrons have to be separated from the pull of the nucleus
They are harder generally because each atom provides two delocalized electrons for the metallic lattice
75
Describe properties of group 7 elements
The Halogens
All the elements are coloured non-metals
All are diatomic molecules (made up of two atoms)
All have 7 electrons in the outermost energy level
All react with metals, forming negative ions
All react with non-metals to form covalent bonds
All react with hydrogen, producing gases which form acidic solutions when dissolved in water
(H2 + Cl2 = 2HCl)
They become less reactive as you go down group
Fluorine is the most reactive since the outermost energy level is nearest to the nucleus. Thus it has the strongest attraction for any electrons in other atoms that are able to form bonds.
A more reactive halogen can displace a less reactive halogen from a solution of its salt
The MP and BP increase as you go down the group because the molecules get larger and therefore the intermolecular forces of attraction increase
76
State the standard state and colour of fluorine (also state the colour of its aqueous solution)
Pale yellow gas (Pale yellow)
77
State the standard state and colour of chlorine (also state the colour of its aqueous solution)
Pale yellow gas (Pale yellow)
78
State the standard state and colour of Bromine (also state the colour of its aqueous solution)
Orange-Brown liquid (Orange-brown)
79
State the standard state and colour of Iodine (also state the colour of its aqueous solution)
Grey-Black solid (Red brown)
80
Describe properties of group 0 elements
The Noble Gas
These are unreactive (inert) gases, since their outermost energy levels are full and cannot gain or lose any electrons
They are therefore monatomic, existing as single atoms instead of molecules
Since they are unreactive, they are used when an inert atmosphere is required
81
Describe properties of transition metals
They have high mp and density (some exceptions e.g. Zn has a low melting point)
They are often used as catalysts
They form coloured compounds
They can have several oxidation states (valences)
82
What is Avogadro's number?
One mole of a substance always conatins 6.23x10^23 number of particles and has a mass known as the atomic mass or the molecular mass.
83
Name the formula for number of moles
Real mass (g) / relative atomic mass
84
What is Avogadro's law or hypothesis>
States that equal volumes of gases at same temperature and pressure contain the same number of particles
85
What is the formula for volume of a substance?
V = moles x 24dm^3
